The Chocolate Chip
Cycle
Topic:
The Rock Cycle
Indiana State Standards:
7.3.9
Explain that sedimentary rock, when buried deep enough, may be reformed by pressure and
heat1, perhaps melting and recrystallizing2 into different kinds of rock. Describe that these
reformed rock layers may be forced up again to become land surface and even mountains,
and subsequently erode.
1
Metamorphic rock
Igneous rock
Note: Footnotes added for clarification purposes. They do not exist in the Indiana State Standards.
2
Materials:
Chocolate: In the form of Chocolate chips, Peanut butter chips, M&M’s, White
Chocolate Chips, Chocolate bars, and any other similar candies.
Hot Plate
Wax paper
Newspaper
Tongs
Plywood 18” x 18”
Goggles
Hot plate
Aluminum pan
Aprons
Aluminum foil
Lesson:
Weathering
Weathering is the process of breaking down rocks. It occurs at or near the Earth’s surface.
There are two types of weathering, Physical and Chemical.
1. Have students cover their work area with newspaper
2. Some materials come as ready made fragments (e.g. chocolate chips). Other materials must
be weathered. Chocolate bars are great for this purpose. Have the students “weather” their
chocolate bars by breaking them into small pieces.
3. The chocolate chips/pieces represent fragments of rock that has been physically weathered.
Pile the fragments by color on separate pieces of wax paper. It often works well if each
student has a different rock type (color). Make sure that the students know they are working
with “weathered” rock material.
4. Depending on class level and remaining time, discuss the questions (attached as an appendix)
or assign questions as homework.
With higher level students it is often good to ask them
about the sizes of fragments. Do we see a variety of sizes in the natural world?
Erosion
Weathering produces loose material that is subject to erosion. Erosion is often defined as the
movement of weathered material. The material is transported by wind, water, or ice. Often, it
accumulates in layers of loose material known as sediment. This is known as deposition. In
addition, stratification can occur when different types of sediment cover one another.
1. Have each group of students place a sheet of Aluminum foil (approx. 10x18) on their work
area.
2. In the center of the foil each student should drop his or her “rock fragments.” This should
be done sequentially i.e. student A then student B etc. When every student has “deposited”
their fragments, have the students examine the pile carefully.
3. Carefully fold the foil over the fragments.
4. Depending on class level and remaining time, discuss the questions (attached as an
appendix) or assign questions as homework.
Lithification and Sedimentary Rocks
Sedimentary rocks are comprised of sediment, which has been lithified. The process of
lithification consists of two parts. First, compaction reduces the size and number of spaces between
fragments. Second cementation “glues” the fragments together.
1. Have students place the foil package between the two pieces of plywood.
2. Have the lightest student in class briefly step onto the board.
3. After removing the package from between the boards, have the students carefully open the
foil and examine the “sedimentary rock.”
4. Have students remove a small piece from the sedimentary rock. The remainder should be left
in the foil package.
5. Depending on class level and remaining time, discuss the questions (attached as an appendix)
or assign questions as homework.
Metamorphism and Metamorphic Rocks
Metamorphic rocks result when preexisting rocks are subjected to heat and pressure.
However, complete melting does not occur. Often, metamorphic rocks appear to have flowed as a
plastic material.
1. Have students place the foil package between two pieces of plywood.
2. Have a heavier student briefly stand atop the board.
3. Briefly place the foil package on a hot plate at low temperature.
4. Repeat steps one through three for an additional three times. Make sure to use the tongs after
the package has been on the hot plate.
a. Note: the temperature of the hot plate is sometimes difficult to identify. Ideally the
temperature should be hot enough to allow the chocolate to flow; however, it
shouldn’t be hot enough to completely melt the chocolate. Every brand of brand of
chocolate chip tends to be different. Thus, some experimentation is required to find
the correct temperature. Furthermore, since we are using different types of chips, it is
not uncommon for them to melt at different temperatures. In the natural world we
also see this with different minerals melting/precipitating at different temperatures.
5. Place the package on the counter and allow it to cool.
6. While the package is cooling, discuss the questions. Have the students predict the answers
for each question
7. Once the package is cool enough to handle, have students open and examine the newly
formed “metamorphic rock.”
8. Place part of the metamorphic rock in an aluminum tray. Store the remaining metamorphic
rock and the previously saved sedimentary rock in a safe place.
9. Depending on class level and remaining time, discuss the questions (attached as an appendix)
or assign questions as homework.
Igneous rock
Igneous rocks are formed from the cooling and solidification of molten rock (magma).
1. Place the aluminum tray atop the hot plate.
2. Carefully adjust the hot plate’s temperature until the “rock” has melted. Be careful that the
chocolate does not splatter. Goggles and Aprons are necessary for this part.
3. Turn off the hot plate and allow the “rock” to cool. Use the tongs to move the tray if
necessary. The tray can be placed atop several layers of newspaper if needed.
4. While the tray is cooling, discuss the questions.
5. Once cooled, have the students compare the previously saved sedimentary and metamorphic
rocks.
Student Questions
Weathering
1. Are all weathered rock fragments in your pile the same size? Why or why not?
2. What have you observed about rock fragments in nature?
3. Where do rock fragments tend to collect?
4. How do rocks get smaller in size?
5. How might ice be an agent of weathering? How about a tree root?
6. Does mechanical weathering differ from chemical weathering? Which type of process does
this activity represent?
Erosion and Deposition
1. Explain your action as an agent of erosion
2. Explain the process of erosion
3. What are deposition and stratification? What are some conditions that might control
deposition?
4. Why are similar-sized rock fragments often found together?
5. Where could you find rock debris fragments in loose layers?
Lithification of Sediment
1. Describe the thickness now compared to when it was initially deposited on the foil
2. What happened to the spaces between the rock fragments?
3. Explain the difference between compaction and cementation
4. Does the activity done here represent compaction of cementation?
Metamorphism and Metamorphic Rocks
1. Describe the color-layer thickness, comparing metamorphic rock with sedimentary rock.
2. Describe the change in fragment shape.
3. Why did this change happen?
Igneous Rocks
1. What happened to the “rock” fragments when they were heated on the hot plate?
2. How does the igneous rock differ from the previously saved sedimentary and metamorphic
rocks? Which type is easiest to break apart? Most difficult?